Physics - Electrostatics

All objects are made of atoms, these consist of neutrons, protons and electrons. If a material has a surfeit (too many) of electrons it becomes negatively charged and if it has deficit (too few) of electrons it becomes positively charged. Since unlike charges attract and like charges repel, this can lead to some interesting effects.

Charging Objects

Before:       Duster = Neutral                           Polythene Rod = Neutral (Equal positive and negative)

As a duster is rubbed on the rod, the electrons are transferred from the duster onto the rod.

After:         Duster = Positive (Since it has lost electrons)        Rod = Negative (Since it has gained electrons)

Bending water

Polythene Rod = Negatively charged   

Water = Positively charged (So negatively rod attracts positive water)

Electrons in the water repelled to this region by the negatively charged rod.

Sticking a balloon to the ceiling

Balloon = Negatively charged                                                Ceiling = Neutral

Negative electrons repelled to the top of ceiling.

Attractive force between negative balloon and positive ceiling.

The more electrons that are added to or removed from an object, the greater the voltage between the object and earth. If this voltage becomes large enough a spark will jump across the gap and equalise the charge.

Lightening

Thunder Cloud = Negatively charged                 Lightening conductor = Positively charged

When lightening occurrs a huge spark is produced as the electrons flow to earth. The lightening conductor is a low resistance pathway for the electrons to reach the earth avoiding damage to the building.

When fuel is been pumped into a fuel tank, the rubbing action of the fuel in the pipe can leave the pipe positively charges and the fuel negatively charge. If the difference in charge is large enough a spark can occur and ignite the fuel. This hazard can be over come by connecting a wire (the bonding line) between the pipe and the tank to allow the charge to equalise.

               Pipe = Positively charged                                     Fuel = Negatively charged